In the design of a semiconductor device, a pipeline circuit as a structure for operating a throughput of input and output with high efficiency can be found.
The pipeline circuit has a multiple-stage circuit structure of processing multiple operating circuits in parallel. Each of the circuits operating in parallel stores a computational result in an intermediate storage area called a pipeline register, and passes this computational result to a circuit in a subsequent stage, thereby implementing a high-performance operation.
Among the circuits having a multiple-stage circuit structure and operating in parallel, a value not used for computation in a circuit in a middle stage needs to be used in a circuit in a subsequent stage. Therefore, the same value not used for computation is copied to a pipeline register in one stage, or pipeline registers over multiple stages. Such a circuit structure in which the same value is copied to a register in one stage or registers over multiple stages, without change, is called a “shift register”.